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Powering from AC adapter — Parallax Forums

Powering from AC adapter

John A. ZoidbergJohn A. Zoidberg Posts: 514
edited 2010-10-17 01:45 in Propeller 1
I noticed that my Propeller experiments with four 7-segments display has resulted in a depletion of 9V batteries really quick - so I might need to use an AC adapter.

I have a LM 7805 w/ heatsink as the 5.0V regulator, but my +3.3V regulator is the one from Holtek and the model is HT1033, without heatsink.

Checked the datasheet for HT1033 - the output current is 20~30mA, while the LM7805 datasheet does not show anything about the output current.

So it is safe to power the system with a LM7805 + HT1033?

By the way the +5V regulated voltage from the LM7805 is fed into the HT1033's input and the HT1033's output is to the Propeller.

Comments

  • LeonLeon Posts: 7,620
    edited 2010-10-16 05:24
    The LM7805 data sheet has the full electrical spec. including max. current.

    I often use an LM317 for 3.3V, or a suitable LDO regulator like the LMS8117.
  • John A. ZoidbergJohn A. Zoidberg Posts: 514
    edited 2010-10-16 07:57
    I see. I only found the max. output current for the National Semiconductor's LM7805, but not in the ST Electronics.

    Since my AC Adapter's is 12V output, I need to get both voltage regulators for 5V and 3.3V which allows 12V. Which could you recommend? :)
  • MacTuxLinMacTuxLin Posts: 821
    edited 2010-10-16 08:15
    I used LM317 to output 10v (used by other circuit) then LM2940 to 5v (used by DS1307+ & others) then LM2937 to 3.3v.
  • kwinnkwinn Posts: 8,697
    edited 2010-10-16 08:27
    MacTuxLin wrote: »
    I used LM317 to output 10v (used by other circuit) then LM2940 to 5v (used by DS1307+ & others) then LM2937 to 3.3v.

    This is a bit of overkill. Any 5V regulator in a TO220 package should be ok when connected directly to 12V. At most a small heat sink may be needed to help with cooling.
  • LeonLeon Posts: 7,620
    edited 2010-10-16 09:09
    John:

    Forget the 12V supply and get a 7.5V ot 9V one. You won't have to mess about with heat sinks.
  • John A. ZoidbergJohn A. Zoidberg Posts: 514
    edited 2010-10-16 09:26
    Leon wrote: »
    John:

    Forget the 12V supply and get a 7.5V ot 9V one. You won't have to mess about with heat sinks.

    I'll search for a 9V adapter in my house. If not, I'll get some of that at a store nearby. :D
  • hover1hover1 Posts: 1,929
    edited 2010-10-16 09:48
    If you can swing the $20 price, the Radio Shack Adapter

    http://www.radioshack.com/product/index.jsp?productId=3875403&numProdsPerPage=60&retainProdsInSession=1

    is an nice 1 amp supply with multiple voltages. It is regulated and filtered. It should come with a free Adapt-a-Plug. Get the "M". It fits all Parallax products.

    Jim
    John A. Zoidberg wrote: »
    I'll search for a 9V adapter in my house. If not, I'll get some of that at a store nearby. :D
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2010-10-17 01:45
    As Leon states, a 9 Volts PSU will help keep down the excess heat. I use a 9V switch mode so the regulators have the luxury of a well setup input, often my 5V reg doesn't have much in the way of heatsink, if any at all.

    A lot of the transformer type wall plug PSUs are unregulated, and dog rough on smoothing, and so have a higher output voltage than the stated one. The stated Volts usually expects the full loading current ( I do not like these types ).

    The regs will expect a minimum input voltage to maintain its regulation, about 2 Volts over the output for the 7805 types. Some of the 3.3V regs have a restricted input range so always check the datasheets (or feed it from the 5V one).
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